2024-07-15Recently, Professor Wang Jianji and others from the green chemistry research team of School of Chemistry and Chemical Engineering of HNU published a research article titled Efficient Capture and Low Energy Release of NH3 by Azophenol Decorated Photoresponsive Covalent Organic Frameworks in the world’s top chemistry academic journal Angewandte Chemie-International Edition (German Applied Chemistry). Tian Xiaoxin, a doctoral student in the School of Chemistry and Chemical Engineering, is the first author of this article, and Wang Jianji, Qiu Jikuan and Wang Huiyong, teachers from School of Chemistry and Chemical Engineering, are co-corresponding authors. Henan Normal University is the first and only corresponding author unit. This study was supported by Key Program of National Natural Science Foundation and Henan Provincial Natural Science Foundation.
Ammonia (NH3) serves as a carbon-free fuel with high hydrogen density but is also a highly toxic environmental pollutant and a major contributor to PM2.5. Consequently, the capture and release of ammonia are crucial for resource utilization of pollutants, development of new energy, and achieving carbon neutrality goals. However, the strong corrosiveness of NH3 and stringent conditions required for desorption make it a technical bottleneck for post-capture reuse. Addressing this challenge, the study presents, for the first time, the integration of photo-responsive azophenol moieties as light-switchable NH3 adsorption sites into the walls of covalent organic frameworks (COFs) through chemical bonding. A UV/visible light-responsive COF named COF-HNU38 (HNU = Henan Normal University) has been designed and synthesized. This material has been applied for efficient NH3 capture and low-energy release. Under UV light, the cis-form of the COF adsorbs NH3 with a capacity of 7.7 mmol g^-1, with approximately 29% of NH3 desorbable by visible light through cis-trans isomerization at ambient temperature and pressure. The remaining NH3 can be desorbed at 25°C and under vacuum; the COF's NH3/N2 selectivity reaches an impressive 158. After eight adsorption-desorption cycles, the photo-responsive covalent organic framework (COF) still exhibits good stability. In situ diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations indicate that multiple hydrogen-bond interactions form between NH3 and the photo-responsive COF. Moreover, the number of hydrogen bonds increases after trans-cis isomerization, with an enhancement in the polarity of the hydrogen-bonding sites, effectively increasing the NH3 capture capacity. Despite the overall strength of the multi-hydrogen bond interactions being quite strong, the strength of individual hydrogen bonds remains relatively weak, which is the main reason for the low-energy release of NH3 molecules.
The study suggests that employing the principles of supramolecular chemistry to design ample adsorption sites capable of weak interactions with ammonia molecules within light-responsive COF micropores could enable remote control over ammonia capture and release. In principle, this could facilitate efficient ammonia sequestration and low-energy desorption, marking another significant advancement by HNU in the field of ammonia capture and low-energy desorption research. This achievement is expected to provide valuable guidance for the design of novel, intelligent ammonia adsorbents.
Paper Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.202406855
(Shi Yunlei, Wang Manman, from School of Chemistry and Chemical Engineering; Wei Ran from Department of Science and Technology)
